This invention relates generally to an active matrix assembly for a liquid crystal display device, and more particularly to an active matrix assembly utilizing a MIS (metal-insulator-semiconductor) transistor array formed on a transparent substrate.
Liquid crystal display devices including active matrixes currently are attracting much attention as the size of the matrix can be increased. This permits enlargement of the display device including a greater number of individual display elements or dots. In view of this, application of the active matrix to a television display is now under serious consideration, since a passive display element for a liquid crystal display has an inherent limitation as to drive duty in the dynamic system.
The dynamic system in the conventional liquid crystal display has a limitation of a 1/16 drive duty. In view of this, it is difficult to display a matrix of dots arranged in 100 rows by 100 columns, or more. However, the active matrix system is known to overcome this drive duty limitation of the dynamic system. In the active matrix system, the switching element or transistor is disposed in a position corresponding to each dot of the display. Additionally, there are known display devices wherein a transistor and a driving electrode for the liquid crystal are formed on a single crystal silicon wafer, or a single crystal silicon film on an SOS substrate. In these latter cases, the liquid crystal material is enclosed between the wafer or the SOS substrate and the upper glass panel. Examples of devices constructed in this manner are shown in the papers in the 1977 Society of Information Display Digest at pages 64-65 and the 1976 SID Digest at pages 76-77. When a transistor is formed on a glass substrate, semiconductor compounds, such as Cd and Se have been utilized for forming the transistor.
The active matrix assembly based on a silicon wafer, or SOS substrate is an expensive raw material for use in a display device. Production and processing costs are expensive. Additionally, the wafer or substrate in these cases is opaque or only somewhat transparent, thereby reducing the display performance. Furthermore, when utilizing one of the semiconductor compounds, the material is poisonous which adds to the processing difficulties. There is also the disadvantage that the semiconductor characteristics are unstable and the reliability of such devices is low.
Accordingly, it is desirable to provide an active matrix assembly for a liquid crystal display device using an MIS (metal-insulator-semiconductor) transistor array on a substantially transparent substrate thereby permitting field effect drive for providing a maximum degree of contrast at low power consumption.